1. Field of the Invention
The invention is a new method of internal combustion engine operation that significantly reduces NO.sub.x and other emissions while maintaining high energy efficiency. The field of application is all internal combustion engines.
2. The Prior Art
The growing utilization of automobiles greatly adds to atmospheric pollution. Reducing emissions, especially NO.sub.x emissions, while maintaining or increasing energy efficiency has been especially difficult.
The two most commonly used piston engines are based on the Otto cycle and the Diesel cycle, respectively. The Otto cycle engine is typical of most engines used in passenger cars and light trucks, while the Diesel cycle engine is typical of engines used in heavier trucks and locomotives and other large engine applications.
The Otto cycle engine has certain characteristics that provide for very low exhaust emissions. The Otto cycle engine is a homogeneous fuel/air inducted engine that is spark ignited and has a piston expander. This engine is operated in an air throttled mode to vary the power produced by the engine while keeping the fuel/air mixture within the flammability limits for the particular fuel. At light and medium loads the homogeneous combustion gives smooth performance and low emission characteristics, but the air throttling reduces efficiency. At higher loads the engine, with exhaust gas recirculation and control to a stoichiometric air/fuel ratio, provides for good engine-out emissions and the opportunity for the exhaust to be routed through a three-way catalyst that further oxidizes the unburned fuel and reduces the oxides of nitrogen that have been formed.
The Diesel engine is characterized by a higher compression ratio, direct fuel injection and the absence of air throttling. The combustion is heterogeneous, and at light and medium loads unburned fuel emissions can be a problem. However, because of its unthrottled nature, in conjunction with the high compression ratio of the engine, the engine operates at a higher efficiency at low and medium loads. However, at higher loads the combustion is at high temperature and a significant amount of oxides of nitrogen is formed. Without the ability to operate the engine in a stoichiometric air/fuel configuration, the ability to utilize a conventional exhaust NOx reduction catalyst is eliminated.